This invention relates to a process for preparing L-fructose alone or in admixture with other L-sugars, such as L-glucose.
L-sugars are useful as sweetening agents because, as disclosed in U.S. Pat. No. 4,262,032, they are sweet like the D-sugars, but unlike D-sugars, L-sugars are either not metabolized by the body or are metabolized to a lesser extent than the D-sugars. These features make L-sugars desirable as sweeteners for individuals wishing to reduce caloric-intake or for individuals unable to metabolize common sugar sweetening agents without detrimental effects, e.g., diabetics. Another advantage associated with L-sugars is the absence of an objectionable aftertaste commonly experienced with artificial sweeteners such as saccharin and the cyclamates. However, as desirable as the L-sugars are in the foregoing respects, their relative scarcity in nature, particularly L-glucose and L-fructose, the laevo counterparts of the two monosaccharide sweeteners most commonly used today, has prevented their widespread use in foods and beverages.
Tomoyeda, et al., "Pentose Metabolism by Candida utilis," Agr. Biol. Chem., Vol. 28, No. 3, pp. 139-143 (1964), the contents of which are incorporated by reference herein, describes the enzymatic isomerization of D- and L-xylose to the respective ketopentoses by employing xylose isomerase isolated from Candida utilis acclimatized on xylose medium.